There is known a method of controlling an adjustable fuel supply apparatus such as a fuel injector, a carburetor or the like to provide a proper fuel supply to an internal combustion engine. In such a fuel supply control method, an amount of fuel supply which is optimum in an operational state of the internal combustion engine is calculated on the basis of various engine parameters representative of operational conditions of the engine.
In the above-mentioned controlling method, a fundamental value representative of the fundamental fuel supply amount is calculated on the basis of the fundamental engine parameters such as the engine rotating speed, the amount of intake air, and so on. The correction coefficient for increase or reduction of the fundamental value is calculated on the basis of the additional engine parameters such as a temperature of the cooling water in the engine, or the transient operational change of engine. A final value representative of a desired fuel supply amount is obtained by multiplying the above-mentioned fundamental value by the above-stated correction coefficient.
In case of a specific operational state of the engine, for example, at a low temperature state of the cooling water or at a high output power state or the like, instead of the feedback control for the theoretical air fuel ratio an air fuel ratio control has to be performed in the open-loop state in the controlling method of the prior-art described above. Whether or not an instantaneous state of the engine requires the open-loop control is determined on the basis of the detected parameters such as the fundamental fuel amount and the cooling water temperature, etc. in a known manner. Moreover, other corrections for increase of the fuel amount are necessary in a specific operational state; thus, it must be determined whether or not the open-loop control is necessary on the basis of those correction coefficients.
As described above, in the prior-art method, a complicated processing is required for discrimination of the necessary of open-loop control. Particularly, for the control using a digital computer, it takes a relatively long time period to complete the aforementioned processing, so that it has been difficult to perform a quick and accurate discrimination.